<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
        <script>
            // window.res
            window.addEventListener('resize',function(){
                // console.log(111);
                // 做响应式
                if(window.innerWidth>800){
                    document.body.style.background='red';
                }else{
                    document.body.style.background='green';
                }
            });
        </script>
</body>
</html>